Hmm... I'm very new to aikido but really enjoying it. This talk of knee problems has me really worried though, since I'm primarily a runner. My knees have felt fine so far, but I know so little aikido that it's not really taxing physically yet, just mentally trying to remember which foot/arm/hand/etc goes where.

Are there any particular exercises or stretches people think would be particularly useful in reducing the chances of a knee injury in aikido?